Biomass Harvesting and Soil Sustainability: Can We Translate Science Into Practice?.

New markets and incentives for wood-derived biomass energy could lead to forest harvesting practices that include greater and more frequent removals of previously non-merchantable biomass.  These practices could degrade forest site productivity, although evidence from field experiments has yet to confirm this as a sound default assumption.  To protect site productivity and other forest values from uncertain but potentially negative impacts, states and other entities are developing biomass harvesting guidelines.  But what does the science tell us about the benefits of such guideline provisions and are they operationally practical?  Factors that should be considered to address these questions include (1) contrasts between experimental harvest treatments and operational harvesting, (2) reliance on conceptual vs. empirical evidence, and (3) prevention vs. correction of negative outcomes.  Experiments such as the Long-Term Soil Productivity and similar studies show striking, visual contrasts between traditional stem-only and whole-tree harvesting treatments.  In an operational context, however, residues from stem-only harvests are rarely distributed evenly across the site and sites where biomass harvesting has been carried out using current technologies are far from clean.  Although even worst-case experimental treatments have not shown consistent, negative impacts on tree growth, underlying impacts on site productivity could arise if repeated biomass removals alter site limitations related to nutrients, water, or physical properties affecting root growth.  Most guidelines are also based on conceptual rather than empirical evidence, which will limit their efficacy and practicality.  In light of current uncertainties, are harvesting restrictions on coarse-textured soils or requirements to retain a specific portion of residues on site justified?  An alternative to preventing any negative outcome is the application of science-based monitoring to detect and correct negative trends or suggest when practices should be modified or limited.  The goal of guidelines should be not only to sustain environmental values but also to avoid complexities and restrictions that limit adoption of a source of energy and biomaterials that is renewable and environmentally beneficial relative to alternatives.